The invention is directed to an expansion dowel formed of an axially extending dowel body and an expansion sleeve. The dowel body has a central through opening with an inner diameter decreasing, at least partly, in the setting direction and with an internal thread as load application means in the region of the through opening at the leading end in the setting direction. Further, the trailing end of the dowel body has a collar extending radially outwardly and the expansion sleeve has a cylindrical inside surface and outside and an outside surface which narrows in diameter at least partly in the setting direction.
Expansion dowels of the type mentioned above are used particularly for hanging intermediate or drop ceilings, paneling, frames, pipes, lines and the like. Since these expansion dowels are set in great numbers, it is particularly required that they can be produced economically and can be placed very quickly and without special effort regarding tools. The expansion dowels are constructed so that one part is formed as a dowel body which serves to absorb or receive the load. By hammering an expansion element into the dowel body, the latter expands in a prepared receiving borehole in rock, concrete, masonry and similar receiving materials. However, they are also used in less hard receiving materials, such as wood.
An expansion dowel of the type mentioned above is known, for example, from DE 195 12 415 A1 and comprises a cylindrical dowel body with a collar and an expansion sleeve. The dowel body has a through opening. The known expansion dowel is expanded by means of the expansion sleeve which is driven into the through opening opposite to the setting direction. In the leading region of the dowel body, the inner diameter surface of the through opening has an internal thread and serves as load application means. To fasten loads, a suitable threaded rod can be inserted into the through opening and screwed into the internal thread. To ensure that the threaded rod is received, the expansion sleeve has an inner diameter that is greater than or equal to the inner diameter of the through opening in the leading region. The known expansion dowel can be set by means of a hammer in a simple manner without additional special setting tools. In addition, the collar provided at the trailing end of the dowel body ensures that the expansion dowel will expand evenly without regard to the depth of the through opening.
A disadvantage of this known expansion dowel is that the threaded rod is anchored in the internal thread of the expansion dowel by screwing in. This screwing in process takes considerable time and accordingly its use is uneconomical.
Further, the length of the threaded rod must be adapted to the application using a fine-tooth saw, for instance, which is very time-consuming. If a bolt cutter is used for this purpose instead of a fine-tooth saw, the threaded end of the threaded rod could be damaged. This causes an additional delay in the screw-in process or might even make it impossible.
It is a primary object of the present invention to provide an expansion dowel which enables a fast and dependable positioning of the threaded rod on the one hand and one that can be produced economically on the other hand.
According to the invention, this object is met in that the dowel body has, in the leading end region in the setting direction, at least a weakened portion which adjoins the internal thread at a distance opposite to the setting direction and acts as an articulation or joint and has at least two axially extending slits which open in the setting direction and extend at least into the region of the weakened portion.
Due to the fact that the internal thread is divided by at least two axially extending slits and a joint into threaded segments which bend radially outward and spring back, it is possible by means of expansion after the expansion dowel is fixed in the receiving material to insert the threaded rod into the through opening up to the desired position by axial pressure in the setting direction. By dispensing with the screw-in process, time is saved on the one hand and there is no substantial damage to the threaded end on the other hand. Accordingly, the length of the threaded rod can be adapted to the application by means of a bolt cutter. When a load acting on the positioned threaded rod opposite to the setting direction is applied, the threaded segments cause the load to be absorbed.
The weakened portion is preferably formed by a circumferentially extending groove. The groove is simple to form in terms of production technique and is accordingly economical.
Advantageously, the groove is arranged at the inside surface of the dowel body. This arrangement of the groove can be produced in one process step while forming the internal thread and results in a further reduction in production costs for the expansion dowel.
Further, preferably the weakened portion can also be achieved through the use of an elastic material at least in the region of the joint, resulting in a greater elasticity of the joint.
In order to ensure the insertion of the threaded rod with a small expenditure of force, the maximum distance corresponds roughly to the diameter of the internal thread.
An optimal holding of the load application means is ensured in that the groove has a depth corresponding to 0.05-times to 3-times the distance of the groove from the internal thread. In this respect, the joint acts as a fulcrum and the thread acts as a force application point. Moreover, in technical respects relating to manufacture, the depth of the groove can be monitored in a simple manner.
Due to the fact that the dowel body and the expansion sleeve are preferably made of plastic, the expansion sleeve can be manufactured economically. Metal can also be used as the material for the expansion dowel.